In the electrophotographic image forming method, an image is usually formed on a transfer sheet via the following processes. That is, charged toner is supplied via contact or non-contact to an electrostatic latent image formed on an electrostatic latent image carrier as an electrophotographic photoreceptor to conduct a developing treatment to visualize the electrostatic latent image, and after transferring the toner image on the electrostatic latent image onto a paper sheet an the like, a fixing treatment is conducted to form a final image.
The developing method to form the toner image on the electrostatic latent image carrier includes a double-component developing method employing a double-component developer composed of a carrier and a toner, and a single-component developing method employing a single-component developer consisting of a toner. In the single-component developing method, charging is conducted by rubbing and pressing the toner with a charging member or the surface of a developing roller without using carrier, whereby it is advantageous to obtain the simplified compact structure of the developing device. Particularly, a non-magnetic single-component developing method is suitably used for color images, and in the case of a full color image forming apparatus equipped with a plurality of developing devices such as those for yellow, magenta, yellow and black toners arranged in a limited space, image formation by the non-magnetic single-component developing method is effective.
The developing roller used for image formation by the non-magnetic single-component developing method, for example, comprises a resin layer placed on a rubber layer provided on the outer circumstance of a shaft, and a thin film of toner is formed on the developing roller by a metal plate or a roller. The thin layer of toner is charged via friction with the foregoing metal plate or the roller.
Therefore, excellent toner conveyance together with a stable charge providing property to toner is demanded for the resin layer formed on the developing roller surface, and a technique by which adhesion or fusion of the toner onto the developing roller surface is prevented has been investigated.
In the case of the thin film formation of toner carried out on the developing roller surface, a large load is applied to the toner as well as the developing roller. The improvement of durability has been desired since peeling is generated because of this unless strong adhesion is provided between the resin layer of the developing roller and a rubber layer. Consequently, a developing roller exhibiting improved durability has been disclosed, in which an intermediate layer is formed on the rubber layer prepared employing a silane coupling agent, and a resin layer formed from a fluorine resin as a principal component is further formed thereon (refer to Patent Document 1, for example).
Further, use of so-called polymerized toner producible while controlling size and shape of toner particles in the course of a manufacturing process becomes enables us to form full color pictorial images (refer to Patent Document 2, for example).
(Patent Document 1) Japanese Patent O.P.I. Publication No. 8-190263
(Patent Document 2) Japanese Patent O.P.I. Publication No. 2000-214629.